Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$237.98	13.448%	$269.9836	$269.98	$270.00	$270.00
Purchase #2	$110.36	9.379%	$120.7107	$120.71	$120.70	$120.70
Purchase #3	$234.53	6.345%	$249.4109	$249.41	$249.40	$249.40
Purchase #4	$143.41	5.186%	$150.8472	$150.85	$150.85	$150.80
Purchase #5	$98.35	7.562%	$105.7872	$105.79	$105.80	$105.80
Purchase #6	$134.51	12.443%	$151.2471	$151.25	$151.25	$151.20
Purchase #7	$164.45	10.439%	$181.6169	$181.62	$181.60	$181.60
7 purchase totals =	$1,123.59		$1,229.6036	$1,229.61	$1,229.60	$1,229.50